Quarks Know Their Left From Their Right | Hacker News Reader

Quarks Know Their Left From Their Right

news.sciencemag.org

43 pointsengassa15 comments

Awesome result. I think it's vitally important to acknowledge achievements that happen in parallel with research at the LHC because otherwise we're going to miss a lot of very neat results. I don't know enough about particle physics to be able to comment on the techniques involved unfortunately, but I love reading about the progress that's being made.

For someone that Wikipedia's a lot of this stuff, does someone know if this type of spin asymmetry is in any sense related to CP violation? [1] As soon as I read the article I thought of CP violation and I'm assuming this is basically the "P" violation.

Finally, reading this article actually triggered a totally different question:

"Using the electron accelerator at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, the researchers shined 170 billion electrons on a target of liquid deuterium over 2 months in 2009."

Shined or shone? Turns out to be quite the discussion topic (e.g., [2][3][4])!

[1] http://en.wikipedia.org/wiki/CP_violation

[2] http://public.wsu.edu/~brians/errors/shined.html

[3] http://grammarist.com/usage/shined-shone/

[4] http://motivatedgrammar.wordpress.com/2010/10/18/has-the-sun...

As it says in the article, this is the discovery of parity, P, violation in a system where it's not been seen before. In a "nice" universe, one might expect mirror images to behave the same, but here they've discovered that interactions between electrons and quarks are different depending on the spin of the electron.

So, it's related to CP violation in the sense that it something "violates CP symmetry" if it's behaviour changes when you flip the charge and the parity of the system simultaneous. Here, they only flip the parity.

For a science magazine, this article does a terrible job of talking about spin. Saying "spinning as it zips along—to the right like a football thrown by a right-handed quarterback or the left like a pigskin thrown by a lefty" is immensely confusing to anyone who actually wants to understand what's going on.

I've seen this trend several places recently.

People are trying to dumb down science so it can be "understandable", often by using sport-analogies. It doesn't help that these dumbed down sport-analogies often feature American sports seldom found in other countries.

The net effect is that if I was in need of a explanation, I'm still confused and all of a sudden annoyed at footballers too.

Spinning ball analogy is very common in school or basic uni.

I think it is spinning ball 100% of the time.

We do not actually know if it physically is spinning. What we know that it behaves like it is spinning.

The problem with science magazines is that if you dumb down paper enough for general public to "understand" it there is basically nothing left.

Article doesn't even try to describe what this $2 C_{2 u} − C_{2 d}$ coupling is all about.

If you're trying to follow High Energy Physics, your best choice is to follow abstracts in ArXiV (which in turn requires _some_ knowledge and education :-(.

Can someone explain what's wrong with the spinning ball analogy? From my understanding, it's a pretty good first approximation of the physical interpretation of particle spin.

Elementary particles are dots for all intents and purposes. But dots can't spin. Spinning requires internal structure to notice spinning, but elementary particles don't have it.

Basically you don't need analogy at all.

Spin is inherent property of a particle like mass, charge, etc. It's quantum like charge. If lagrangian of interaction includes particle's spin, spin effects will be noticeable in scattering and everywhere.

Analogy is only needed to not mix spin with angular momentum.

Funny how in media spin is left and right, but in science spin is always "up" or "down". :-)

Agreed, but you will also agree that you've gone well beyond the level of first approximation here, right?

Maybe. :-)

This analogy has quite a lot of problems which arguably can confuse more than explain.

First thing my physics professor said in uni was "forget everything you've learned in school". This is applicable to spinning balls.

Well, for one thing it uses slang which is probably only vaguely recognizable to the majority of the non-American English-speaking world. And for another thing, it relies on a fact which I (starter on the (American) football team for five years during junior high and high school) didn't know. I mean, it makes sense that the two throwing styles would produce spins in the opposite direction, but I had to stop and think about it.

Which is why I have so much respect for Richard Feynman. His books, especially QED, are so well written that I could understand the most part while still being able to appreciate the complexities. I believe he has said something to the effect of "if I can not make a lay person understand complex phenomenon it only means I have not understood it fully yet.

Staying on topic, Feynman found it hard to explain spin.

> Feynman was a truly great teacher. He prided himself on being able to devise ways to explain even the most profound ideas to beginning students. Once, I said to him, "Dick, explain to me, so that I can understand it, why spin one-half particles obey Fermi-Dirac statistics." Sizing up his audience perfectly, Feynman said, "I'll prepare a freshman lecture on it." But he came back a few days later to say, "I couldn't do it. I couldn't reduce it to the freshman level. That means we don't really understand it."

If Feynman couldn't do it, perhaps it's okay to give a pass on how spin is described in this article?

Quarks don't know anything and they don't spin like a football, bad science reporting is bad science reporting.

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